The fermented alcohol produced from carbohydrates such as sweet potato, potato, corn, etc. is an important material for making various drinks and for industrial applications. Because alcohol concentration produced by fermentation is as low as 10.about.20 wt %, it is necessary to condense it to about 95.about.100 wt %.
Conventionally, the distillation method has been used for this concentration. However, this method is economically disadvantageous because much energy is consumed in heating the water--main component of this material--to 80.about.100.degree. C., and there is a strong demand on the development of an energy-saving method of concentration to replace the conventional means.
On the other hand, it has been proposed to use the energy-saving method to extract, separate and concentrate alcohol from water, using carbon dioxide in supercritical or pseudocritical condition. (Japanese provisional patent publications No. 56-56201 and 59-141528).
However, there is some restrictions to the selective extraction of alcohol when carbon dioxide is used as solvent. Maximum concentration is limited to about 91 wt %, and it is impossible according to the recent report to condense beyond this limit. Also, a large quantity of carbon dioxide (more than 15 weight parts of CO.sub.2 to 1 weight part of 10% aqueous solution of alcohol) is needed because the solubility of alcohol in carbon dioxide is not high enough, and it is earnestly wanted to solve this problem.
As the result, there is a strong demand on the development of a new method and an apparatus to increase alcohol concentration and to raise alcohol solubility.
The purpose of the present invention is to provide the economical method and apparatus to concentrate and purify alcohol, by which it is possible to increase alcohol concentration to more than 91 wt% and to concentrate and recover alcohol by the use of small quantity of solvent.